Washington HVAC Glossary of Terms
The HVAC sector in Washington State operates under a layered vocabulary that spans mechanical engineering, state code, utility program requirements, and licensing classifications. Fluency with these terms is essential for contractors, inspectors, property owners, and regulators navigating the state's permitting and compliance landscape. This glossary defines the core terminology used across residential, commercial, and industrial HVAC contexts as they apply under Washington State law and the Washington State Energy Code and related regulations.
Definition and scope
HVAC — an acronym for Heating, Ventilation, and Air Conditioning — encompasses the mechanical systems that control thermal comfort, humidity, and indoor air quality in built environments. In Washington, HVAC work is regulated primarily by the Washington State Department of Labor and Industries (L&I), which administers contractor licensing under RCW 18.27 and mechanical permits under the Washington State Mechanical Code (WAC 51-52).
The glossary below organizes terms into five functional clusters: system components, performance metrics, regulatory and permitting terms, refrigerant classifications, and ventilation standards.
System component terms
Air Handler Unit (AHU): The indoor cabinet assembly containing the blower, heating or cooling coil, and filter rack. In split systems, the AHU circulates conditioned air through the duct network.
Condenser: The outdoor unit of a split-system air conditioner or heat pump. It rejects heat absorbed from indoor air to the outside atmosphere through a refrigerant-to-air heat exchange process.
Evaporator Coil: The indoor coil where refrigerant absorbs heat from return air, producing the cooling effect. Paired with the condenser in split systems.
Heat Pump: A refrigeration-cycle device capable of reversing flow to provide both heating and cooling. Washington's climate profile makes heat pumps the dominant residential system type; coverage of their operational requirements appears in the Washington heat pump systems overview.
Ductless Mini-Split: A split-system without a central duct network. One outdoor unit connects to between 1 and 8 indoor air-handling heads via refrigerant lines. Popular in Western Washington retrofits where duct installation is impractical. System-specific detail is covered in Washington ductless mini-split systems.
Furnace / Air Handler: A forced-air heating appliance using gas combustion or electric resistance. The dominant heating source in Eastern Washington where natural gas distribution infrastructure is more prevalent.
Geothermal Heat Pump (Ground-Source Heat Pump): A heat pump that exchanges thermal energy with the ground or a water body rather than outdoor air, yielding higher efficiency coefficients in climates with large seasonal temperature swings.
Performance metric terms
SEER2 (Seasonal Energy Efficiency Ratio 2): The cooling efficiency metric adopted by the U.S. Department of Energy (DOE) effective January 1, 2023. SEER2 replaces the original SEER rating and uses a revised M1 blower external static pressure test condition of 0.5 inches water gauge (in. w.g.), producing ratings approximately 5% lower than equivalent SEER values.
HSPF2 (Heating Seasonal Performance Factor 2): The heating efficiency metric for heat pumps under the 2023 DOE test update. Minimum HSPF2 for heat pumps sold in the Northern climate region (which includes Washington) is 7.5 (DOE Federal Register, January 2023).
EER2 (Energy Efficiency Ratio 2): A single-point cooling efficiency ratio measured at 95°F outdoor dry-bulb temperature under the revised M1 test conditions.
COP (Coefficient of Performance): A dimensionless ratio of useful thermal energy output to electrical energy input. A heat pump with a COP of 3.0 delivers 3 watts of heating per watt of electricity consumed.
Manual J Load Calculation: The ACCA (Air Conditioning Contractors of America) standard methodology for calculating the peak heating and cooling load of a conditioned space. Washington's HVAC system sizing guidelines require Manual J compliance for permitted installations.
Static Pressure: The resistance to airflow in a duct system, measured in inches water gauge (in. w.g.). Proper duct design targets total external static pressure within the equipment manufacturer's rated range.
Regulatory and permitting terms
Mechanical Permit: Authorization issued by a local Authority Having Jurisdiction (AHJ) before HVAC installation or replacement work begins. Required under WAC 51-52 for most new equipment installations in Washington.
Authority Having Jurisdiction (AHJ): The code official, inspection department, or organization responsible for enforcing applicable codes. In Washington, this is typically the county or city building department, operating under state-adopted codes administered by the Washington State Building Code Council (SBCC).
Certificate of Occupancy (CO): A document issued by the AHJ confirming that a structure — including its mechanical systems — complies with applicable codes after inspection.
Washington State Energy Code (WSEC): The energy efficiency requirements adopted by the SBCC and codified in WAC 51-11C (commercial) and WAC 51-11R (residential). The WSEC sets minimum equipment efficiency, envelope performance, and commissioning requirements. Full regulatory context is available in Washington energy efficiency standards for HVAC.
TD-1 Contractor License: The Washington L&I license classification for contractors performing HVAC-related work under the Contractor Registration Act (RCW 18.27). Specific licensing classifications and examination requirements are detailed in Washington HVAC licensing and certification standards.
Refrigerant classification terms
HFC (Hydrofluorocarbon): The refrigerant family that includes R-410A and R-32. HFCs have zero ozone depletion potential (ODP) but high global warming potential (GWP). The U.S. Environmental Protection Agency (EPA) is phasing HFCs down under the AIM Act of 2020.
A2L Refrigerant: A classification under ASHRAE Standard 34 denoting mildly flammable refrigerants with low burning velocity (≤ 10 cm/s) and low heat of combustion (≤ 19 kJ/g). R-32 and R-454B are A2L refrigerants replacing R-410A in new equipment. Installation requirements for A2L systems involve specific leak detection and ventilation protocols under ASHRAE 15.
R-410A: The dominant residential refrigerant from approximately 2010 through 2024. Production restrictions under the AIM Act begin phasing manufacturers away from R-410A equipment. Washington-specific refrigerant handling obligations are described in Washington HVAC refrigerant regulations.
EPA Section 608 Certification: Federal certification required of all technicians who purchase or handle regulated refrigerants under 40 CFR Part 82. Four certification types exist: Type I (small appliances), Type II (high-pressure systems), Type III (low-pressure systems), and Universal.
Ventilation terms
ASHRAE 62.2: The ANSI/ASHRAE standard specifying minimum ventilation rates for acceptable indoor air quality in residential buildings. Washington's residential energy code references ASHRAE 62.2 for whole-building and local exhaust requirements.
ASHRAE 62.1: The companion standard for commercial and institutional buildings, specifying ventilation rates per occupant and per unit floor area by space type.
ERV (Energy Recovery Ventilator): A mechanical ventilation device that transfers heat and moisture between exhaust and supply airstreams, recovering 70–80% of conditioned energy from exhaust air. Common in Washington's high-performance residential construction under the WSEC.
HRV (Heat Recovery Ventilator): Similar to an ERV but transfers heat only, without moisture exchange. Better suited to heating-dominated climates where excess interior humidity is undesirable.
CFM (Cubic Feet per Minute): The volumetric airflow unit used in duct design, equipment rating, and ventilation calculations throughout North American HVAC practice.
How it works
HVAC terminology functions as a shared technical language across the five parties involved in any Washington HVAC project: the property owner, the licensed contractor, the equipment manufacturer, the local AHJ, and the utility program administrator. Miscommunication between these parties — particularly on efficiency metric versions (SEER vs. SEER2), refrigerant classifications, or permit scope — is the most common source of project delays and compliance failures.
A structured understanding of these terms follows a logical hierarchy:
- Equipment classification — identify the system type (heat pump, furnace, mini-split, geothermal) and its refrigerant category.
- Efficiency metrics — confirm which rating system (SEER2, HSPF2, COP) governs the product, and verify it meets WSEC minimums.
- Load calculation — Manual J sizing determines equipment capacity in BTU/h (British Thermal Units per hour).
- Permit requirements — determine whether a mechanical permit is required from the local AHJ before work begins.
- Inspection and commissioning — post-installation inspections confirm code compliance; commissioned equipment logs verify measured airflow and static pressure align with design.
The Seattle HVAC Authority provides city-specific reference on contractor qualifications, permit processes, and equipment selection within Seattle's jurisdiction, where the Seattle Department of Construction and Inspections (SDCI) administers local mechanical permits under the Seattle Mechanical Code — a locally amended version of the state code.
Common scenarios
Scenario 1 — Permit confusion on equipment replacement: A property owner replaces a like-for-like